I diagnosed a problem on my 1990 Miata to the ISC valve. Looks like a
simple part to replace...but wait! How about around $500 for a new one?
This thing must employ precious metals; it's like buying a part for a
This can't be the only one that failed. Has anyone else bit the bullet
I helped another person on here a while back with the ISC valve on a
1990 model. Is this the valve that is located in the throttle body? I
remember having trouble determining exactly which part it was, but I may
have access to another one.
$500.00 is insane, that is a big percentage of the blue book value of
the entire car.
Do you have a picture of the valve by any chance?
Thanks, Pat...that's very kind of you to offer.
I bit the bullet and ordered a new one. In the interest of perhaps
helping someone else, I took images and posted them here:
The first three images are of the throttle body and ISC valve attached.
The next two show the parts disconnected with the gasket placed between
them. The last three are different views of the ISC valve.
Generally, I have found the parts for my '90 Miata to be reasonably
priced. I understand that rationale of charging a premium for
replacement parts; part of it is certainly legit but you are correct to
point out that some gouging exists.
The good news is that the Miata fails so rarely. So when it comes to
shelling out a few shekels for a clutch slave cylinder or a rear brake
caliper, it isn't all that tough to take.
I would think one reason is that they are manufactured in small amounts.
That drives the price up greatly, because design and tooling must be
paid for by much smaller numbers and the lowest cost manufacturing methods
are not economical at such series.
Leon van Dommelen :) Bess, the Miata :) Bozo, the Miata :)
The idle was too fast. It was OK when the engine was cold and would not
settle down when hot. This was intermittent for a while, then it was
consistent (idle fast when hot). This is one of the troubleshooting
scenarios covered in the Workshop Manual.
There is a simple test for the ISC which is to remove the connector and
re-install it. A "click" is supposed to result (it did not). Next step
is to measure the resistance between the terminals. At nominal
temperatures, it should read around 12 ohms. Mine reads infinite ohms
There may be other symptoms of an ISC failure, but this is what happened
to my car.
Roland Smith wrote:
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